1. Field of the Invention
The present invention relates to a technique for performing, in an optical apparatus such as a video camera, a digital camera, a television camera, or an interchangeable lens, focus detection or focusing control by utilizing an output from a photoelectric converting element.
2. Description of the Related Art
In recent years, many image-taking apparatuses such as consumer video cameras have been mounted with auto-focusing (hereinafter, referred to as AF) apparatuses. The conventional AF apparatus extracts a signal corresponding to the sharpness (contrast) of an object image from an image-pickup signal and evaluates the signal to perform a focusing operation with an optical system has become the mainstream.
A configuration example to realize this type of AF method will be described by use of FIG. 7. In the same drawing, Reference Numeral 101 denotes a focus lens contained in an image-taking optical system, and Reference Numeral 102 denotes an actuator for driving the focus lens 101. Reference Numeral 103 denotes a CCD, and Reference Numeral 104 denotes a read-out timing generating section which generates timing of reading out pixel information from the CCD 103.
Reference Numeral 105 denotes a process section to process output signals from the CCD 103 and prepare the output signal into a format for NTSC signals (or PAL signals) or the like, and Reference Numeral 106 denotes an AF region timing generating section which generates a signal to designate a pixel region (hereinafter, referred to as an AF evaluating region) read out to evaluate a focus state of an image-taking optical system by use of horizontal and vertical synchronizing signals from the read-out timing generating section 104.
Reference Numeral 107 denotes a luminance signal extracting section which extracts a luminance component from an output signal which is output from the CCD 103, and Reference Numeral 114 denotes a high-frequency component extracting section which receives a luminance signal from the luminance signal extracting section 107 and extracts, in terms of luminance components, a high-frequency component by use of a bandpass filter or the like.
Reference Numeral 115 denotes an evaluating value generating section which generates, in terms of output signals within an AF evaluating region determined by a signal from the AF region timing generating section 106, an evaluating value used for a focusing judgment such as a maximum output value or an added value of maximum values of the high-frequency component extracting section 114 in field cycle units. Reference Numeral 112 denotes an AF drive control section which controls the actuator 102 according to a result of the evaluating value generating section 115.
Next, operations of the above-described configuration will be described. An object image formed by a light flux passed through the focus lens 101 is projected on an image-pickup surface of the CCD 103, and is photoelectrically converted by the CCD 103. An output from the CCD 103 is read out by a read-out timing signal of a read-out timing generating section 104 and is inputted into the process section 105. In the process section 105, input signals are processed into an image format for NTSC signals or the like, and these image signals are outputted to a recording unit or an output terminal.
On the other hand, output signals of the CCD 103 are also transmitted to the luminance signal extracting section 107. In the luminance signal extracting section 107, a luminance signal component is generated from the inputted signals and is outputted to the high-frequency component extracting section 114. In the high-frequency component extracting section 114, a horizontal high-frequency component is extracted by a bandpass filter or the like. The extracted high-frequency component information is, in the evaluating value generating section 115, processed into an evaluating value required for AF operations in field cycle units.
In general, an evaluating value whose value increases as an edge component of the image is enhanced is generated, such as a maximum value of signals within an AF evaluating region designated by a signal from the AF region timing generating section 106, a sum of maximum values of respective horizontal lines within the AF evaluating region or the like.
In terms of the evaluating value generated as such, a comparison judgment is made in the AF drive control section 112 in field cycle units. And, in order to maximize the evaluating value, the focus lens 101 is driven via the actuator 102.
Here, as an image-taking apparatus to perform such AF control, a focusing apparatus proposed in Japanese Patent Application Laid-Open No. H8(1996)-265620 exists.
According to the above-described a conventional focusing apparatus, since a focusing judgment is made based on a high-frequency component of an image signal, namely, an edge component information, for example, with an attempt of taking an image of an object including a high-luminance light source (shown as a white outline region in the drawing) as shown in the left drawing of FIG. 2(A), a point where the edge component maximizes appears in a defocus state where no entity exists, and a focusing judgment is made in the defocusing state as in the left drawing of FIG. 2(B).